select: add poll_select_set_timeout() and poll_select_copy_remaining() helpers

This patch adds 2 helpers that will be used for the hrtimer based select/poll:

poll_select_set_timeout() is a helper that takes a timeout (as a second, nanosecond
pair) and turns that into a "struct timespec" that represents the absolute end time.
This is a common operation in the many select() and poll() variants and needs various,
common, sanity checks.

poll_select_copy_remaining() is a helper that takes care of copying the remaining
time to userspace, as select(), pselect() and ppoll() do. This function comes in
both a natural and a compat implementation (due to datastructure differences).

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Arjan van de Ven <arjan@linux.intel.com>

1 files changed, 75 insertions, 0 deletions

diff --git a/fs/select.c b/fs/select.c
index da0e88201c3a..1180a6207789 100644
--- a/fs/select.c
+++ b/fs/select.c
@@ -130,6 +130,81 @@ static void __pollwait(struct file *filp, wait_queue_head_t *wait_address,
         add_wait_queue(wait_address, &entry->wait);
 }
 
+/**
+ * poll_select_set_timeout - helper function to setup the timeout value
+ * @to:         pointer to timespec variable for the final timeout
+ * @sec:        seconds (from user space)
+ * @nsec:       nanoseconds (from user space)
+ *
+ * Note, we do not use a timespec for the user space value here, That
+ * way we can use the function for timeval and compat interfaces as well.
+ *
+ * Returns -EINVAL if sec/nsec are not normalized. Otherwise 0.
+ */
+int poll_select_set_timeout(struct timespec *to, long sec, long nsec)
+{
+        struct timespec ts = {.tv_sec = sec, .tv_nsec = nsec};
+
+        if (!timespec_valid(&ts))
+                return -EINVAL;
+
+        /* Optimize for the zero timeout value here */
+        if (!sec && !nsec) {
+                to->tv_sec = to->tv_nsec = 0;
+        } else {
+                ktime_get_ts(to);
+                *to = timespec_add_safe(*to, ts);
+        }
+        return 0;
+}
+
+static int poll_select_copy_remaining(struct timespec *end_time, void __user *p,
+                                      int timeval, int ret)
+{
+        struct timespec rts;
+        struct timeval rtv;
+
+        if (!p)
+                return ret;
+
+        if (current->personality & STICKY_TIMEOUTS)
+                goto sticky;
+
+        /* No update for zero timeout */
+        if (!end_time->tv_sec && !end_time->tv_nsec)
+                return ret;
+
+        ktime_get_ts(&rts);
+        rts = timespec_sub(*end_time, rts);
+        if (rts.tv_sec < 0)
+                rts.tv_sec = rts.tv_nsec = 0;
+
+        if (timeval) {
+                rtv.tv_sec = rts.tv_sec;
+                rtv.tv_usec = rts.tv_nsec / NSEC_PER_USEC;
+
+                if (!copy_to_user(p, &rtv, sizeof(rtv)))
+                        return ret;
+
+        } else if (!copy_to_user(p, &rts, sizeof(rts)))
+                return ret;
+
+        /*
+         * If an application puts its timeval in read-only memory, we
+         * don't want the Linux-specific update to the timeval to
+         * cause a fault after the select has completed
+         * successfully. However, because we're not updating the
+         * timeval, we can't restart the system call.
+         */
+
+sticky:
+        if (ret == -ERESTARTNOHAND)
+                ret = -EINTR;
+        return ret;
+}
+
+
+
 #define FDS_IN(fds, n)          (fds->in + n)
 #define FDS_OUT(fds, n)         (fds->out + n)
 #define FDS_EX(fds, n)          (fds->ex + n)